The invention relates to an automatic decompression device for valve-controlled internal-combustion engines, and more specifically to an automatic decompression device for use in the internal-combustion engine of a motorcycle.
One example of an automatic decompression device is disclosed in U.S. Pat. No. 5,687,683. The device includes a decompression lever pivotally mounted on a camshaft and having a pivot axis that is situated at a right angle to the rotational axis of the camshaft. The decompression lever has two lever arms configured such that the center of gravity of the lever is fixed on the rotational axis of the camshaft or immediately adjacent thereto.
The decompression lever is acted upon by a spring member, so that below a specified rotational speed of the camshaft, the decompression lever is kept in a first position and engages a valve. In this first position, automatic decompression is achieved by suitable actuation of the valve as the camshaft rotates. If a predetermined rotational speed of the camshaft is exceeded, the decompression lever is pivoted against the spring force into a second position as a result of the action of centrifugal forces. In the second position, there is no longer an operative connection between the decompression lever and the valve, and therefore no automatic decompression.
As is evident from the drawings of the ""683 Patent, the decompression lever is coupled to the camshaft in between the ends of the camshaft and in the region of a cam. To achieve this configuration, the camshaft and the cams are provided with corresponding recesses that are adapted to receive the lever.
The recesses provided in the camshaft and cams of the prior art assembly can result in the weakening of the camshaft and the cams, which are both highly stressed components of the internal combustion engine. The present invention overcomes this problem and provides an improved automatic decompression device for valve-controlled internal-combustion engines in which the decompression lever is fastened or mounted in such a way that the strength and rigidity of the cams and the camshaft are not adversely affected. More specifically, the decompression lever is mounted on an end face of the camshaft such that neither the cams nor the camshaft have their strength or rigidity adversely affected. With this design, the number of manufacturing steps is reduced and assembly is facilitated.
More specifically, the invention provides an automatic decompression device for an internal combustion engine. The device includes a camshaft rotatable about an axis of rotation and having an end face, and a lever coupled to the end face and movable between a first position, wherein the lever is engageable with a valve actuating device to actuate a valve during rotation of the camshaft, and a second position, wherein the lever does not substantially move the valve actuating device.
In one aspect of the invention, the lever is pivotally coupled to the end face to pivot about a pivot axis that is substantially perpendicular to the axis of rotation of the camshaft. In another aspect of the invention, the automatic decompression device further includes a spring between the end face and the lever to bias the lever toward the first position. In yet another aspect of the invention, the end face of the camshaft includes a slot and the lever is at least partially retained within the slot.
In yet another aspect of the invention, the automatic decompression device further includes a cam mounted adjacent the end face of the camshaft. The cam has an end face that is engaged by the lever when the lever is in the second position. Preferably, the end face of the cam includes a groove having therein a stop, and the lever includes an arm that engages the stop when the lever is in the second position. Further preferably, the engagement between the stop and the arm is a line contact to substantially prevent the arm from sticking or binding in the groove.